org.apache.pig.impl.plan
Classes 
CompilationMessageCollector
CompilationMessageCollector.Message
DependencyOrderWalker
DepthFirstWalker
DotPlanDumper
MapKeysInfo
NodeIdGenerator
Operator
OperatorKey
OperatorPlan
OperatorPlan.IndexHelper
PlanDumper
PlanVisitor
PlanWalker
ProjectionMap
ProjectionMap.Column
RequiredFields
ReverseDependencyOrderWalker
Enums 
CompilationMessageCollector.MessageType
Exceptions 
PlanException
PlanValidationException
VisitorException